Mechanical Testing and Validation of MRI-Derived Finite Element Models

Daniel looking at an MRI image on a computer.




Assistant Professor of Radiology

Project Summary

This past summer I had the opportunity to dive further into research as part of the Laboratory for Structural, Physiologic and Functional Imaging (LSPFI) in the Perelman School of Medicine. Our research was primarily focused around the current insufficient methods of diagnosing osteoporosis. Presently, DXA standards are the primary measure for diagnosing osteoporosis, which are determined by a single measure for bone mineral density (BMD). Measuring by BMD alone fails to account for the internal microarchitecture of bone, and as a result many patients that are at risk of sustaining a hip fracture are underdiagnosed. One method for determining the true strength of bone is by simulating how bone would break under a fall. Simulations by finite element analysis (FEA) derived from CT scans of the femur have been validated, however CT scans expose patients to harmful ionizing radiation. A less harmful alternative that we explored this summer is by using MRI scans to develop models in place of CT.

I was primarily focused on producing accurate simulations of hip models derived from MRI imaging. This was a highly technical process that involved multiple steps. First, the scans of bone were segmented to produce models. Second, we needed to determine values for bone marrow intensity and cortical bone in order to distinguish bone from non-bone in the simulation. Third, we ran the simulations and compared to direct mechanical testing of the same cadavers that we obtained MRI scans of. I also helped conduct the analysis between the mechanical data and values produced from running FEA. After we found that simulating by MRI-derived models was predictive of mechanical strength, we also developed a plan to further validate our methods by comparing to microCT derived models. We are currently in the process of creating the models from the microCT scans and testing via FEA. Lastly, I also investigated a relatively novel method of MRI called ultrashort echo time (UTE) imaging. In traditional MRI, only liquid and fat content of bone regions can be measured, and bone is determined from areas in which there is no signal received. This is because the signal from bone decays too quickly for it to be captured by the MRI machine. In UTE, the echo time between the pulse emitted by the MRI machine and the detection of the signal is short enough that data from bone (T2) species is able to be captured. This is significant because data about the actual quality of bone, instead of simply the presence or absence of bone can be obtained. We are currently working to develop new models utilizing UTE technology, which I am excited to continue to be a part of.

I am extremely grateful that I was granted the opportunity to focus in on the intricacies of this type of research this summer, since this is something that can be difficult to do during the school year while balancing other classes and responsibilities. I look forward to continuing my involvement in research throughout my life.